Traditionally, batch processes have been used for continuous polymerization in the manufacturing of yarn and other products which are costly and time consuming, as well as lack in product uniformity. For example there is viscosity variation from batch to batch and also during polymer extrusion from the reactor into strands, leading to poor spinning, also leading to high pressure rise across the filters in the polymer lines and spinning packs, high spinning breaks per tonne and poor post processing performance (broken filaments on textured bobbins). Some methods do mention use of a continuous process with different variations such as the use of additives with the accompanying polymerization temperature, spin pack pressure, less uniformity and higher filament breakage rate.
Cationic dyeable polyester (PET) has been conventionally made by introducing (during polymerization) as a comonomer    a) the sodium salt of 5, sulfoisophthalic acid dimethyl ester (abbreviated SIPM)or    b) in case of PTA process for PET, after transesterification (catalyzed by sodium acetate etc) of SIPM with excess ethylene glycol to the sodium salt of 5, sulfoisophthalic acid diglycolate (abbreviated SIPE or SIPEG)
JP 2002-284863 suggests that SIPEG (or SIPM) charge may give a gel with high acid groups in PTA slurry and cationic dyeable polyester PTA route is more complex. (DMT or PTA route)
U.S. Pat. No. 6,706,852 suggests that to provide increased compatibility with the glycol end-group carrying oligomer (such as BHET) in the PTA route, transesterification of SIPM with MEG to SIPEG is carried out in the PTA route.
Fully or part conversion from SIPM to SIPEG is recommended by some. JP 2002-284863 and EP 1862488 recommend full conversion; U.S. Pat. No. 6,706,852 recommends part conversion to address the issue of solution stability (vs. crystallization-precipitation).
High concentration of SIPEG in MEG is desired to reduce MEG removal load on the polymerization reactor and to reduce recycle of the excess solvent in the process. U.S. Pat. No. 6,706,852 suggested that fully converted SIPEG solution is not stable at high concentration (40% or higher) at room temperature. Therefore it needs to be prepared (i.e. SIPM to SIPEG conversion) immediately before use in polymerization. Else, either a lower concentration of less than 20% should be employed, or a partial conversion to SIPEG should be adopted.
Also point of addition of TiO2 and SIPM/SIPEG, due to the anticipated interaction between the two plays an important role in the reaction. Section [0019] of JP 2002-284863 suggests that the SIPEG charge may give gel with high acid groups in slurry, hence better add later in reaction when carboxylic acid concentration has fallen. JP 2002-284863 suggests feeding SIPEG in slurry. Similarly, EP 1862488 talks about various modes, but section [0043], [0048] and [0057] there suggest preference for addition to slurry. However, that does require adjustment of pH of the slurry. JP 2002-284863 and EP1862488 suggest TiO2 addition in slurry immediately after SIPEG. U.S. Pat. No. 6,706,852 also recommend TiO2 addition immediately following SIPEG, but in oligomer from PTA. U.S. Pat. No. 5,559,205 instead recommends TiO2 addition to oligomer, and before SIPEG, to avoid agglomeration of TiO2.
Also, the MEG to PTA mole ratio is critical for good spinning. of JP 2002-284863 and the EP 1862488 suggest use of MEG not exceeding 1.2 to avoid excess DEG to avoid spinning problems in continuous polymerization.
JP 2002-284863 and [0051] in EP 1862488 suggest solving the problem of high viscosity/thickening (resulting from aggregation of ionic/charged parts of SIPEG, and deteriorating spinning/giving gelling) with addition of PEG. [0035] of this patent says only 280 deg C. is used. EP1862488 under [0030] also mentions that PEG reduces heat resistance of polyester, and reduces color tone. EP1862488, under [0057] item 5 sets temp not higher than 280 deg C. Also [0010] of EP 1862488, it introduces the additional problem that “dark-color light fastness” becomes unsatisfactory (because PEG introduces somewhat ‘open’ structure in fiber). This EP 1862488 also claims dyeability at low temp/normal pressure, essentially because of the PEG, a well known effect. JP 2002-284863 under [0025] also suggests that PEG introduces undesirable foaming possibility during polymerization.
Batch processes as disclosed in the U.S. Pat. No. 6,706,852, employ agitated vessel for carrying out polymerization with SIPM/SIPEG. But polyester manufacturing in large continuous plants has largely moved to reducing/eliminating moving parts (such as agitators) in reactors, particularly the esterifier and prepolymerizer, in an effort to reduce process costs (CAPEX and OPEX). U.S. Pat. No. 5,559,205 suggests additive addition is generally carried out in ‘oligomer line’ leading from esterifier to prepolymerizer U.S. Pat. No. 5,559,205 mentioned need for TiO2 to be well-mixed in oligomer without mentioning how to achieve this as they only ‘metered-in’ the slurry, perhaps with some static mixers, but the later addition of SIPEG simply by ‘metering-in’ into the oligomer line. No mention of need for particularly good dispersion of TiO2 in the TiO2-MEG slurry itself prior to addition to the PTA-MEG slurry.
Also in U.S. Pat. Nos. 6,706,852 and 6,075,115, it is common knowledge to use phosphoric acid or another phosphorus compound in process using SIPEG is to control the polymer discoloration, particularly when using Ti catalyst as it slows down the catalytic activity of Ti. It teaches that sometimes H3PO4 is not effective and other polymers may perform better. In another application JP 2001-086169 of Kanebo Synthetic Fibers Ltd, discloses a method for producing atmospheric cationic dyable polyester. It suggests an improvement over existing methods but has many drawbacks such as the spinning operatibility is remarkably bad, light fastness is inferior and the degree of polymerization is low.
JP58-45971B and JP62-89725 disclose batch polymerization methods. If a batch type manufacturing method is used it will extrude by aging of polymer extrusion, will extrude with the polymer viscosity at the time of a start and a difference will arise in the polymer viscosity at the time of the end. When the number of batches increased, there was a problem that the foreign matter in which residual polymer in an iron pot deteriorated mixed or the polymer property difference between the batches became large. Hence the problem of productive efficiency remains with batch processes.
JP62-146921A suggests a method of extracting oligomer after the end of esterification, leading to another polymerization tank, using continuous polymerization method directly as the above-mentioned measure and manufacturing by the batch type polymerizing method. Since the polymerization reaction serves as a batch method, there are spots of polymer physical properties and there is also a problem that equipment becomes complicated. It also suggests use of additive like PEG which limits polymerization temperature to 285 deg C. Similarly [0030] of EP 1862488 suggests that PEG reduces heat resistance and color tone of polyester and EG:PTA mole ratio of 1.1-1.2. This gives remarkably bad spinning operatibility. [0058] of EP1862488 suggests need of light resistant and heat resistant agents. Also spinning breakage rate is remarkably higher in this art.
U.S. Pat. No. 5,559,205 discloses a process for adding fully esterifted bis(2-hydroxyethyl) sodium 5 sulfoisophthalate (Na-SIPEG) or bis(2-hydroxyethyl) lithium 5-sulfoisophthalate (Li-SIPEG) to the monomer line of DMT process, or oligomer line or the second esterifier of TPA process to make cationic dyeable polyesters. This patent does not allow addition of TiO2 in slurry and do not specify need of addition of SIPEG into oligomer. SIPEG is added after TiO2 addition. Also no reference is made about “continuous process” thus limiting the performance.
U.S. Pat. No. 6,075,115 discloses a process for making Na-SIPEG solution and Li-SIPEG solution from sodium 5-sulfoisophthalic acid (Na-SIPA) and lithium 5-sulfoisophthalic acid (Li-SIPA) powder. In order to fully esterify Na-SIPA and Li-SIPA, a special titanium catalyst 65 is used, which comprises (1) a titanium compound, a solubility promoter, a phosphorus source, and optionally a solvent or (2) a titanium compound, a complexing agent, a phosphorus source and optionally a solvent, a sulfonic acid. The fully esterified Na-SIPEG and Li-SIPEG solutions were manufactured by a vendor and then shipped to polyester producers. The solution was then injected into the monomer line of DMT process or oligomer line or the second esterifier of TPA process or the second or third vessel of batch polymerization process to make copolyesters. A metal salt of 5-sulfoisophthalic acid fully esterified with methanol is also commercially available. This process makes no mention of continuous process or injection into oligomer line. Also batch process is employed here and TiO2 is not added in slurry. Also problems of spinning are evident. Hence there is long standing need for faster continuous method of polymerization.
Patent No. U.S. Pat. Nos. 7,087,706 and 4,110,316 suggest use of static mixers in the transfer line for mixing of additives while agitated mixing equipments are generally avoided in order to eliminate chance of process disturbances. However, the chances of gel formation are higher in such vessels. This problem is not addressed by existing methods.